New constraints on upper-mantle S-velocity structure and crustal thickness of the Iranian plateau using partitioned waveform inversion

The continental collision between the African and Eurasian plates resulted in a tectonically young and complex deformation in the Iranian plateau. The present-day Iranian plateau is characterized by diverse tectonic domains including the continental collisions (e.g. Zagros and Alborz) and the oceanic plate subduction (e. g. Makran). Partitioned waveform inversion method is used here to image the S-velocity structure of the upper-mantle and Moho-depth variations in the Iranian plateau. Of nearly 3000 waveforms originally selected for the analysis, we have fitted 974 waveforms from 101 events and 39 stations which result in 11 688 linear constraints on the upper-mantle S-velocity structure and Moho depth for the region. Our new seismic images show seismically faster upper mantle beneath the Zagros and the Arabian Plate compared to the Central Iran and Alborz. This high-velocity anomaly has descended beneath the Central Iran along the Main Zagros Thrust. Across the Zagros collision zone, the tomographic images show a slab stagnation in the transition zone (at about 410 km depth) in the form of a horizontal high-velocity zone which does not penetrate the deeper parts of the mantle. The lowest S-velocities are concentrated beneath the Central Iran and Alborz. According to our velocity models, a strong high-velocity anomaly is resolved beneath the trapped South Caspian Basin with clear indication of westward underthrusting beneath the Talesh and western Alborz. In Makran, southeast Iran, there is a clear evidence of subduction of oceanic crust of the Arabian plate beneath the Makran belt which is correlated with seismicity pattern across the Makran zone. Also, the inverted Moho map using a priori information of crustal thickness constraints shows the large crustal thickness beneath the Zagros suture zone (in some places to a maximum depth of 65 km) which indicates the influence of crustal thickening and shortening beneath Arabian-Eurasian Plate boundary. A significantly crustal thinning is observable across the South Caspian Basin compared to its margins.